Optical communication systems employ optical amplifiers, e.g., to compensate for signal attenuation in optical fibers. One type of amplifier that may be used in a fiber-based communication system is an OPA. As known in the art, an OPA is a device that produces a tunable coherent optical output via a nonlinear optical processes called four-wave mixing (FWM), in which two photons from one pump wave, or two pump waves, are destroyed and two new photons are created, with conservation of the total photon energy and momentum. The waves corresponding to the two new photons are usually referred to as the signal wave and the idler wave. This process amplifies a weak input signal and generates an idler, which is a frequency converted (FC) and phase-conjugated (PC) image of the signal. As known in the art, there is another type of FWM process, in which one signal photon and one pump photon are destroyed, and one idler photon and one different pump photon are produced, with conservation of the total photon energy and momentum. This process transfers power from the signal to the idler, which is a FC image of the signal. Optical frequency converters, OFCs, can be used to perform switching and routing in communication systems. The fundamentals of FWM are discussed in a book by G. P. Agrawal [“Nonlinear Fiber Optics, 3rd Edition,” Academic Press, 2001, hereafter referred to as GPA].
However, a problem with two-pump OPDs is the SRS noise that appears in the output signals and idlers. Because of SRS noise, the output signals or idlers produced by OPDs have lower signal-to-noise ratios (SNRs) than the input signals, which reduces the effectiveness of OPDs in communication systems.